1. Field of the Invention
The present invention relates to a magnetic tunnel effect type magnetic head having a magnetic tunnel junction element sandwiched with conductive gap layers between a pair of magnetic shielding layers, and a recorder/player adapted to record and/or play back a signal to and/or from a magnetic recording medium by the use of the magnetic tunnel effect type magnetic head.
2. Description of the Related Art
It is well known as a so-called magnetic tunnel effect that in a laminated structure having a thin insulative layer sandwiched between a pair of magnetic layers, when a predetermined voltage is applied between the pair of magnetic layers, the conductance of a so-called tunnel current varies depending upon the relative angle of magnetization between the pair of magnetic layers. That is, the laminated structure having the thin insulative layer sandwiched between the pair of magnetic layers shows a magneto-resistive effect to the tunnel current flowing through the insulative layer.
With the magnetic tunnel effect, it is possible to theoretically calculate the magneto-resistive coefficient or ratio between the pair of magnetic layers owing to the polarizability of the magnetic layers when magnetized, and more specifically, to have a magneto-resistive coefficient or ratio of about 40% in case the pair of magnetic layers is formed from Fe.
Thus, as a magneto-resistive effect element, the magnetic tunnel junction element (will be referred to as “TMR element” hereunder) having a laminated structure having a thin insulative layer sandwiched between a pair of magnetic layers has been attracting the attention in the field of this art. Especially in the field of magnetic heads, attention is focused on a so-called magnetic tunnel effect type magnetic head (will be referred to as “TMR head” hereunder) using the TMR element as a magneto-sensitive element to detect a magnetic signal from a magnetic recording medium.
Referring now to FIG. 1, there is schematically illustrated such a conventional TMR head by way of example. FIG. 1 is a schematic end view of the TMR head from a recording medium side. The TMR head is generally indicated with a reference 100.
As shown in FIG. 1, the TMR head 100 is a so-called shielded TMR head having a TMR element 104 sandwiched with a gap layer 103 between a pair of upper and lower magnetic shielding layers 101 and 102. The TMR head 100 is of a laminated structure in which the above component elements are formed on a substrate 105 by the thin-film laminating process. In the TMR head 100, the pair of magnetic shielding layers 101 and 102 functions as electrodes for the TMR element 104. There are sandwiched between the pair magnetic shielding layers 101 and 102 nonmagnetic conductive layers 106 and 107 of the gap layer 103 which electrically connect the pair of shielding layers 101 and 102 and the TMR element 104 to each other. Also, in the TMR head 100, a part of the TMR element 104, abutting a projection 107a of the nonmagnetic conductive layer 107, serves as a magnetic sensor portion 104a of the TMR element 104. The magnetic sensor portion 104a has a reading track width of Tw.
Referring now to FIG. 2, there is schematically illustrated a conventional shielded MR (magneto-resistive) head by way of example. FIG. 2 is a schematic end view of the MR head from a recording medium side. The MR head is generally indicated with a reference 200. As shown in FIG. 2, the MR head 200 has an MR element 204 and a pair of upper and lower conductive layers 205 and 206 formed at either end of the MR element 204, sandwiched with a gap layer 203 between a pair of upper and lower magnetic shielding layers 201 and 202. The MR head 200 is of a laminated structure in which the above component elements are formed on a substrate 207 by the thin-film forming process. In the MR head 200, a part of the MR element 204, laid between the pair of conductive layers 205 and 206, serves as a magnetic sensor portion 204a of the MR element 204. The magnetic sensor 204a has a reading track width of Tw.
In the shielded MR head 200, as the gap is decreased for a higher recording density, the nonmagnetic nonconductive layer which forms the gap layer 203 is thinner. More specifically, because of steps formed by the pair of conductive layers 205 and 206 disposed on the opposite ends of the MR element, it is difficult to form the upper nonmagnetic nonconductive layer to a uniform thickness over the MR element 204. In case the distance between the pair of magnetic shielding layers 201 and 202 and the MR element 204, that is, the inter-shield distance, is decreased for reading a signal recorded with a high density in a magnetic recording medium, it is extremely difficult to secure an insulation between the pair of magnetic shielding layers 201 and 202 and the MR element 204.
On the contrary, in the TMR head 100 shown in FIG. 1, the pair of magnetic shielding layers 101 and 102 function as electrodes so that the gap layer 103 can be made thin and thus the distance between the pair of magnetic shielding layers 101 and 102 and the TMR element 104 can be decreased. Therefore, in the TMR head 100, the gap can be made narrow to enable a high density of recording to a magnetic recording medium.
For production of the above-mentioned TMR head 100, a generally disc-like substrate is prepared, the component elements of the TMR head 100 are formed one on the other on the substrate by the thin-film forming process, and then the substrate is cut into individual head chips, thereby producing a plurality of TMR heads 100 collectively.
However, in the process of producing the TMR head 100, the nonmagnetic conductive layers 106 and 107 forming together the gap layer 103 are elongated without being polished, when the height of the TMR element 104 in the direction of its depth is adjusted by polishing it on a surface plate, so that the pair of magnetic shielding layers 101 and 102 sandwiching the TMR element 104 between them will electrically be short-circuited between them as the case may be. That is, a defect 108 is caused in the medium-opposite face of the produced TMR head 100 by the elongation of the nonmagnetic conductive layers 106 and 107 in some cases as shown in FIG. 3.
In this TMR head 100 thus produced, no current will flow through the magnetic sensor portion 104a of the TMR element 104 and little playback output will be detected from the magnetic recording medium.